The present invention relates generally to a steam turbine and more particularly to a support bar design that supports a steam turbine diaphragm while housed in a steam turbine casing and that facilitates reduced maintenance cycle time and cost of the steam turbine.
A typical steam turbine generally includes static nozzle segments that direct steam flow into rotating buckets that are connected to a rotor. Each row of buckets and their corresponding nozzles is known as a turbine stage. The nozzle construction is typically called a turbine diaphragm stage. A turbine diaphragm is assembled into two halves (i.e., an upper half and lower half) around a rotor, creating a horizontal joint. The turbine diaphragm is supported vertically by one of several possible approaches at the horizontal joint. One approach is to use a support bar to vertically support the turbine diaphragm while it is housed in a turbine casing, which also is assembled into halves separated by a midline. In this approach, there are typically two support bars that are attached to the bottom half of the turbine diaphragm near the horizontal joint by several horizontal extending bolts.
Current support bar designs have been found to hinder the maintenance cycle time and cost of a steam turbine because these designs require that the rotor and diaphragm lower half be removed in order to perform vertical diaphragm alignment or maintenance on the turbine diaphragm. As a result, a typical turbine diaphragm maintenance process may take several shifts or days to complete. In such a turbine diaphragm maintenance process, an upper casing from the turbine assembly is first removed. Then, the upper half of the turbine diaphragm is removed. The support bars cannot readily be removed from the turbine diaphragm without removing the diaphragms from the turbine casing because there is not enough clearance to get to the horizontal bolts that are used to horizontally secure the support bars to the lower half of the diaphragm. The fact that the support bars cannot be removed from the diaphragms while in the turbine casing means that the adjustment shim blocks also cannot be removed, therefore, preventing vertical adjustment of the diaphragm within the turbine casing. Thus, the rotor needs to be removed to allow access to the shim block for vertical diaphragm adjustment.